Exposure to toxic agents, such as CW agents and related toxins, is a potential hazard to the armed forces and to civilian populations, since CW agents are stockpiled by several nations, and other nations and groups actively seek to acquire these materials. Some commonly known CW agents are bis-(2-chloroethyl)sulfide (HD or mustard gas), pinacolyl methylphosphonofluoridate (GD), Tabun (GA), Sarin (GB), cyclosarin (GF), and O-ethyl S-(2-diisopropylamino)ethyl methylphosphonothioate (VX), as well as analogs and derivatives of these agents, and any additional nerve or vesicant agents. These CW agents are generally delivered as fine aerosol mists which, aside from presenting an inhalation threat, will deposit on surfaces of military equipment and hardware, including uniforms, weapons, vehicles, vans and shelters. Once such equipment and hardware is contaminated with one of the previously mentioned highly toxic agents, the agent must be removed in order to minimize contact hazards.
For this reason, there is an acute need to develop and improve technology for decontaminating highly toxic materials. This is especially true for the class of toxic agents known as nerve agents, which are produced and stockpiled for both industrial use and as CW agents. One class of nerve agents with a high level of potential lethality is the class that includes organophosphorus-based (“OP”) compounds, including, but not limited to, Sarin, Soman, and VX. Such agents can be absorbed through inhalation and/or through the skin of an animal or person. The organophosphorus-type (“OP”) CW materials typically manifest their lethal effects against animals and people by inhibiting acetylcholine esterase (“AChE”) enzyme at neuromuscular junctions between nerve endings and muscle tissue to produce an excessive buildup of the neurotransmitter acetylcholine, in an animal or person. This can result in paralysis and death in a short time.
In addition to the concerns about CW agents, there is also a growing need in the industry for decontaminating industrial chemicals and/or insecticides, for example, AChE-inhibiting pesticides such as parathion, paraoxon and malathion, among others. Thus, it is very important to be able to effectively detoxify a broad spectrum of toxic agents, including, but not limited to, organophosphorus-type compounds, from contaminated surfaces and sensitive equipment.
Furthermore, CW agents and related toxins are so hazardous that simulants have been developed for purposes of screening decontamination and control methods. HD simulants include 2-chloroethylethyl sulfide (CEES) and 2-chloroethylphenyl sulfide (CEPS). G-agent simulants include dimethyl methyl phosphonate (DMMP). VX simulants include O,S-diethyl phenylphosphonothioate (DEPPT).
Currently, the U.S. Army uses a nerve agent decontamination solution called DS2, which is composed (by weight) of 2% NaOH, 28% ethylene glycol monomethyl ether, and 70% diethylenetriamine (Richardson, G. A. “Development of a package decontamination system,” EACR-1 310-17, U.S. Army Edgewood Arsenal Contract Report (1972), incorporated by reference herein). Although this decontamination solution is effective against OP nerve agents, it is quite toxic, flammable, highly corrosive, and releases toxic by-products into the environment. For example, a component of DS2, namely diethylenetriamine, is a teratogen, so that the manufacture and use of DS2 also presents a potential health risk. DS2 protocol calls for waiting 30 minutes after DS2 application, then rinsing the treated area with water in order to complete the decontamination operation. The use of water in the operation presents logistics burdens, as now large volumes of water must be transported and stockpiled at the decontamination site.
The U.S. Army also uses a decontamination material called XE555 resin (Ambergard™ Rohm & Haas Company, Philadelphia, Pa.), to remove toxic agents from the contaminated surface as rapidly as possible. However, XE555 has several disadvantages. Although effective at removing chemical agents, XE555 does not possesses sufficient reactive properties to neutralize the toxic agent(s) absorbed by this resin. Thus, after use for decontamination purposes, XE555 itself presents an ongoing threat from off-gassing toxins and/or vapors mixed with the resin. In addition, XE555 is relatively expensive in the quantities required for decontamination purposes.
Meanwhile, reactive sorbents have been developed and used to both absorb and react with highly toxic materials to yield less toxic products. One example is M100 sorbent decontamination system (SDS) for decontaminating highly toxic materials. The M100 SDS utilizes an alumina-based reactive sorbent called A-200-SiC-1005S, which is in the form of a powder. The reactive sorbent powder acts as an inexpensive, non-corrosive, non-harmful absorber designed to be rubbed onto a contaminated surface and does not require water rinse or special disposal. The reactive sorbent is structured to flow readily across a contaminated surface, and is highly porous, allowing it to absorb the highly toxic material quickly. The absorbed highly toxic material is strongly retained within the pores of the reactive sorbent, which reacts to form less toxic products, thereby minimizing off-gassing and contact hazards. Details of this sorbent are provided in U.S. Pat. No. 6,852,903.
Another example is U.S. Pat. No. 5,689,038, to Bartram and Wagner, disclosing the use of an aluminum oxide, or a mixture of aluminum oxide and magnesium monoperoxyphthalate (MMPP), as reactive sorbents to decontaminate surfaces contacted with droplets of chemical warfare agents. It has been reported that both materials were able to effectively remove such toxic agents from a surface to the same extent as XE555. In addition, both materials represented improvements in chemical warfare agent degrading reactivity and in reducing off-gassing of toxins relative to XE555. The reported sorbents were based on pre-existing, commercially available materials, such as Selexsorb CD™, a product of the Alcoa Company. Essentially, Bartram and Wagner reported that their aluminum oxide is modified by size reduction, grinding or milling.
Another example is U.S. Pat. No. 6,537,382 to Bartram and Wagner, disclosing the use of two types of reactive sorbents. One comprises metal exchanged zeolites such as silver-exchanged zeolite, and the other comprises sodium zeolites. The reactive sorbents remove, and then decompose chemical agents from the surface being decontaminated. Similar in all reactive sorbents, this dual action provides the advantage of reducing the risks associated with potential off-gassing from the sorbent, and reducing the toxicity of the sorbent for disposal purposes.
However, inasmuch as the above-mentioned solid-phase decontaminants are able to quickly remove CWAs from surfaces, they suffer from slow reactions with the adsorbed agents. Once contaminated, these sorbents present a persistent hazard themselves following their use. The hazard is particularly acute for VX, the most persistent and toxic of these agents, where half-lives ranging from several hours to several days (and even months) are not uncommon.
Recently, two notable improvements on absorbing and removing VX have been reported. The first by Wagner, Wu, and Kleinhammers (U.S. patent application Ser. No. 11/668,524 “Nanotubular Titania for Decontamination of Chemical Warfare Agents”; and Wagner, G. W.; Chen, Q.; Wu, Y. “Reactions of VX, GD, and HD with Nanotubular Titania J. Phys. Chem. C 2008, 112, 11901-11906) discloses that VX reacts rapidly with nanotubular titania (NTT). This material affords VX half-lives on the order of several minutes (Wagner, G. W. unpublished results). A second titania material, nanocrystalline titania (nTiO2), exhibits an even faster VX reactivity, allowing half-lives less than 2 minutes (Wagner, G. W. “Decontamination Efficacy of Candidate Nanocrystalline Sorbents with Comparison to SDS A-200 Sorbent: Reactivity and Chemical Agent Resistant Coating Panel Testing” ECBC-TR-724, in press; unclassified report).
Still, there remains a need in the art for even more rapid and effective sorbents for decontaminating toxic agents, and the methods for rapidly and effectively removing and/or decontaminating toxic agents in an environmentally acceptable and cost-effective process.